Graphite Experiment Shines New Light On Giant Planets, White Dwarfs and Laser-Driven Fusion
Posted: 29 November 2012 02:12 PM   [ Ignore ]
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This information directly applies to dpf devices.

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Posted: 29 November 2012 02:49 PM   [ Ignore ]   [ # 1 ]
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How so?  The ion heating in a plasma focus is derived from the kinetic energy of the fast moving ions rather than electron heating of the ions which is more like the case for laser fusion and tokameks.  PF devices and Z-pinches are one of the few devices that allow the ion temperature to exceed the electron temperature.  In any case, PF fusion as described in literature relies on instability driven ions more like a particle accelerator rather than a thermal bath of ions fusion like in a tokamek or laser fusion pellet.  In my way of thinking a cold ion and electron population may actually be a good thing as the kinetic pressure of the plasma is lower so you can compress more mass as long as you can still generate the fast ions you need, you win. 

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Posted: 29 November 2012 05:52 PM   [ Ignore ]   [ # 2 ]
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I have some questions.
How do you measure the relative temperatures of ions versus electrons in a plasma?
If free hot electrons in a plasma have little temperature effect on ions, then does it matter if there is some radiation loss from the electrons?

Is the proposed onion device a charge collection unit for high speed electrons or a photoelectric unit?  If it is a photoelectric unit it should be able to capture the radiation loss from hot electrons.  That would mean that anything from high powered lasers to x-ray machines should be able to test the onion concept.  An appropriately equipped university lab could design and test a unit with the energy spectrum of a dpf.  Maybe it could be a thesis project.

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Posted: 29 November 2012 08:14 PM   [ Ignore ]   [ # 3 ]
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Electron temperature is typically measured using the relative line ratio in emission spectrum of characteristic lines or by measuring the bremsstrahlung continuum shape.  The ion temperature is measured from the broadening of spectral lines, typically in the x-ray.  Sandia National Lab had a huge affair a few years back about 200 keV ion temperatures in iron plasmas.  There is a PRL published by Malcolm Haines of Imperial College about it.  The debate about the source rages to this day. 

Electron heating and cooling:  To get an ion hot, you must undergo many, many collisions with electrons that have more energy but each transfer is small because of momentum conservation so only a fraction of the electron population can supply energy to the ion.  In the case of cooling, the electrons collide with the ion and take a fraction of the energy.  The electrons radiate the energy away as brems when they slow.  Those greedy electrons go back for more.  While many electrons take away energy only some can provide it.  The electrons also transport energy (heat) very efficiently as they are highly mobile.  A typical pinch has a temperature profile with the temperature peaked near the center.  If electrons are able to move, they transport that heat out of the core plasma to the edge. 

The general rule of plasma is the electrons are the dominate particles for energy transport, radiation and current carrying.  The ions are responsible for momentum carrying and mass.  These rules are pretty universal.  Pinches are a bit funny as the ions have such large kinetic energies before the pinch implodes which allows them to have large ion temperatures when the pinch stagnates on axis.  Other plasma systems cannot give the ion much energy as they are slow to respond to electric fields unlike electrons and they are so heavy.  The PF allows the ions to move quickly due overwhelming magnetic pressure behind the plasma sheath that pushes both the ions and electrons at the same speed.  If an ion moves at the same speed as an electrons but has 2000X the mass, it has 2000X the energy.  Easy to see how the ion can have higher temperatures than the electrons in a pinch.  The thermalization is complex so don’t read too much in the 2000X number upfront.  Those pursuing fusion wish that cold electrons could coexist with hot ions. 

Can’t speak to the onion or LPP’s plans for it.

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Posted: 29 November 2012 08:44 PM   [ Ignore ]   [ # 4 ]
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The reason we want to minimize radation emitted by electrons is because it cools the plasma. too much cooling and the plasma will not heat itslef up to pB11 temperatures. Yes, we do intend to catch the x-ryas emitted with the onion, but we need to minimize the x-rays anyway because of cooling. The onion requires signifcant engineering input, so I doubt it could be a thesis project.

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